The invention generally relates to an apparatus for the galvanic deposition of a metal layer on a substrate and, more particularly, to a galvanic deposition apparatus having an adjustable substrate holder and anode exit surface.
An apparatus of this kind is used, for example, for the galvanoplastic production of compression tools or molds, especially ones made of nickel. These compression tools are used for the compression molding or injection molding of disks, such as compact disks (CDs), laser vision disks and other information-carrying disks. The above-mentioned molds, which include original molds, as an example, molds known as a "glass master", as well as reproductions thereof, are intermediate molds for producing the compression tools. The surface of the molds carry information in the form of a relief or recess. The surface structure is transferred to the compression tool by means of galvanoplastic reproduction. The information contained in this surface structure is imprinted onto the surface of a plastic material when using the compression tool for injection molding or compression molding. In optical disks, such as compact disks, the relief structure modulates the light of a laser beam such that the information imprinted on the surface of the disk can be read.
To produce the compression tools or the molds, a metal layer, usually nickel, is deposited on a substrate that is either an insulating substrate like glass plus a thin electrically conductive layer, or a metal substrate, comprising for example nickel. In either case, the substrate surface has a relief-like structure that contains the information to be read. The smallest information unit, called a "pit," has a spatial wave-length in the micrometer range. The pits are arranged in information tracks and the distance between adjacent information tracks is also in the micrometer range. Since the substrate surface may contain several billion (10.sup.9) information units, and these corresponding fine structures in the micrometer range have to be transferred to the metal layer, the galvanic metal deposition process has to meet very high standards. The deposited metal layer should be extremely small grained and free of tension and the thickness of the deposited layer should be relatively large. For example, the compression tool produced by metal deposition for producing compact disks should have a thickness of 295 .mu.m.+-.5 .mu.m. In addition, the deposition process should be carried out at a high speed. Moreover, the apparatus for galvanic deposition should be small in size and simple in its operation.
Another important requirement when creating galvanoplastic metal layers on a substrate is that the thickness of the deposition layer should be uniform across the entire substrate surface. The thickness should vary only within close limits. If these limits are not met, the optical disks produced by means of this metal layer will be of a lesser quality.
A galvanic deposition apparatus of the type described above is known from EP-A-O 058 649. The apparatus includes an anode container filled with an anode material and inclined with respect to a vertical line. The exit surface of the anode container is essentially parallel to a substrate surface. The substrate is supported by a substrate holder driven by a shaft. But, the metal layer deposited on the substrate by means of this known apparatus shows considerable variations in the thickness of the layer across the substrate surface.
Thus, it is an object of the present invention to provide an apparatus for the galvanic deposition of a metal layer in which the variations in the thickness of the layer is reduced across a relatively large surface of the substrate.